The present invention relates to a nozzle for coating a flat disc with a thin film of a lubricant, and more particularly to a nozzle for so coating a disc while the disc is in a horizontal position.
There has been recently developed a high density recorded disc, i.e. a video disc, in which the recorded information is in the form of a surface relief pattern formed along a spiral path on the major surface of the disc. Preferably, the surface relief pattern is formed in a spiral groove in the major surface of the disc. The recorded disc is played with a stylus which has a very fine tip which rides in the groove. In order to reduce frictional forces and to prevent wear of the stylus and/or the disc, a very thin layer, preferably between 200 and 400 Angstroms thick, of a lubricant is provided on the surface of the disc.
One apparatus and method for coating a disc with a thin layer of a lubricant is shown and described in U.S. Pat. No. 4,309,456 to B. E. Lock, issued Jan. 5, 1982, entitled "Method and Apparatus for Coating Recorded Discs With a Lubricant," which is incorporated herein by reference. In the method of this patent, droplets of the lubricant are formed in an atomizer chamber by passing streams of air through the lubricant. The air then carries the lubricant droplets from the atomizer chamber to nozzles in a coating chamber. The nozzles direct the lubricant droplets onto the surfaces of a disc which is carried between the nozzles. In the apparatus shown, the disc is in an upright vertical position and the nozzles direct the lubricant droplets horizontally onto the surface of the disc. However, it has now been found to be more desirable to have the disc in a horizontal position and arrange the nozzles to direct the lubricant droplets vertically downwardly onto the surface of the disc as the disc passes under the discharge opening of the nozzle. However, having the nozzle in a vertical position has raised a problem in that those lubricant droplets that contact the inner surface of the nozzle tend to stick to the inner surface of the nozzle. The droplets collect and coalesce, and will then flow down the inner surface of the nozzle forming large droplets that drip onto the surface of the disc. Any such large drops of the lubricant on the surface of the disc forms a much thicker film than desired and interferes with the proper playback of the disc.